1. Field of the Invention
The present invention relates to a method for manufacturing a liquid ejection head capable of simplifying the manufacturing process and excellent in reliability.
In this Specification, a word “print” refers to not only forming a significant information, such as characters and figures, but also forming images, designs or patterns on a printing medium and processing such as etching and so forth in the printing medium, whether the information is significant or insignificant or whether it is visible so as to be perceived by humans. The term “printing medium” includes not only paper used in common printing apparatus, but also sheet materials such as cloths, plastic films, metal sheets, glass plates, ceramic sheets, wood panels and leathers or three-dimensional materials such as spheres, round pipes and so forth which can receive the ink. The word “ink” should be interpreted in its wide sense as with the word “print”, refers to liquid that is applied to the printing medium for forming images, designs or patterns, processing such as etching in the printing medium or processing such as coagulating or insolubilizing a colorant in the ink and includes any liquids used for printing.
2. Description of the Related Art
As a conventional art, an ink-jet printing method disclosed in Japanese Patent Application Laid-open No. 54-51835(1979) is characterized in that a driving force for ejecting a liquid droplet is obtained by applying a thermal energy to the liquid, which is different from other ink-jet printing methods. That is, according to this ink-jet printing method, the liquid subjected to the operation of the thermal energy is vaporized to generate air bubbles. The expansion force accompanied with the growth of the bubbles makes liquid droplets to be ejected from an orifice of a printing head to a printing medium so that a predetermined image information such as characters or images is printed on the printing medium. The printing head used for this ink-jet printing method generally includes an nozzle orifice for ejecting the liquid, a liquid chamber communicating with the nozzle orifice, for storing the liquid to be ejected, an ejection energy generator disposed in the liquid chamber, for generating the thermal energy for ejecting the liquid droplet from the nozzle orifice, a protecting layer for protecting the ejection energy generator from the liquid, and a heat storage layer for storing the thermal energy generated from the ejection energy generator.
Also, in Japanese Patent Application Laid-open No. 10-13849(1998), a method is disclosed, for forming, by an anisotropic etching, a liquid supply port communicating with the above-mentioned liquid chamber to supply the liquid to this liquid chamber. In Japanese Patent Application Laid-open No. 10-181032(1998), a method is disclosed, for forming the liquid supplying port more precisely by further using a sacrificial layer. In this Japanese Patent Application Laid-open No. 10-181032(1998), a concrete process performed by the sacrificial layer during the high-precision etching is described in the explanation of a first embodiment with reference to FIGS. 1 to 3.
One example of a process for manufacturing the liquid supply port in the conventional printing head described above will be described with reference to FIGS. 27 to 34 based on the technique disclosed in Japanese Patent Application Laid-open No. 10-181032(1998) as follows. A SiO2 layer 2 is formed by oxidizing the surface of a silicon substrate 1 and deposits a Si3N4 layer 3 thereon by a reduced pressure CVD method (see FIG. 27). Then, a patterning is carried out to leave the Si3N4 layer 3 solely in the vicinity of a region in which a sacrificial layer 4 described later is formed. At this time, all of the Si3N4 layer 3 deposited on the rear surface of the silicon substrate is removed by the etching during the patterning (see FIG. 28). Next, the silicon substrate 1 is further heat-oxidized to grow the SiO2 layer 2. At this time, a portion disposed directly beneath the patterned Si3N4 layer 3 is not oxidized but solely the SiO2 layer 2 disposed on the opposite sides thereof is selectively oxidized, whereby a thickness of the SiO2 layer 2 not covered with the Si3N4 layer 3 increases. Thereafter, the Si3N4 layer 3 is removed by the etching (see FIG. 29). Then, to form a sacrificial layer 4 of polysilicon, a portion of the SiO2 layer 2 having a thin film thickness because this portion has been covered with the Si3N4 layer 3 is removed by the etching, and instead, the sacrificial layer 4 of polysilicon is formed in this portion (see FIG. 30). Next, an etching-stop layer 5 encircling this sacrificial layer 4 is formed of Si3N4 which stress is adjusted by the reduced pressure CVD method, and a whole surface thereof is covered with a phospho-silicate glass (PSG) layer 6 (see FIG. 31). Further, a second SiO2 layer 7 is formed on the PSG layer 6 by a plasma CVD method (see FIG. 32), and the SiO2 layer 7 and the PSG layer 6 are patterned, after which a second Si3N4 layer 8 reaching the etching-stop layer 5 is formed all over a surface thereof by the plasma CVD method (see FIG. 33). Thereafter, a liquid supply port 9 extending from the rear surface side of the silicon substrate 1 to the sacrificial layer 4 is formed by the anisotropic etching (see FIG. 34).
Japanese Patent Application Laid-open No. 2003-136492 discloses that if the sacrificial layer is formed of polysilicon by the same process as a film-forming process or an etching process for a gate electrode of a MOS transistor in a drive circuit or others, an exclusive mask for the sacrificial layer becomes unnecessary.
However, since a resistivity of polysilicon is generally high, it is necessary to lower the resistivity when used as the gate electrode of the transistor, for example, by doping impurity. On the other hand, since an etching speed of polysilicon doped with impurity is liable to lower, it is unsuitable for using polysilicon as a material for the sacrificial layer which needs the etching speed higher than that of a material to be etched. Accordingly, when the electrode and the sacrificial layer are formed of the same material; polysilicon; for the purpose of saving the manufacturing process, one or both of the electrode and the sacrificial layer may be lower in performance, whereby it is impossible to merely use the polysilicon as it is.
Further, since the PSG layer may be dissolved by an etching liquid when the PSG layer is provided on a wiring layer such as a gate electrode, there is a case that it is unsuitable as an anti-etching layer. For example, when a predetermined portion of the PSG layer 6 is etched as one of processes shown in FIGS. 32 to 33 for supplying the liquid fed from a lower part of the substrate via the liquid supply port 9 to an upper part of the substrate, the sacrificial layer 4 is directly exposed to the etching liquid unless the etching-stop layer 5 covering the sacrificial layer 4 is separately provided.
In the prior art, to avoid such a problem, the etching-stop layer 5 formed of Si3N4 is provided between the sacrificial layer 4 and the PSG layer 6. Accordingly, in a case wherein the PSG layer is provided on the wiring electrode, an anti-etching layer of silicon nitride used as the etching-stop layer is formed in a structure around the liquid supply port before the PSG layer is provided, so that the etching of the PSG layer is possible without affecting the sacrificial layer of polysilicon.
Also, since the anti-etching layer of silicon nitride must be heated at a predetermined temperature when formed by the reduced pressure CVD method, polysilicon is used for the sacrificial layer formed together with the wiring layer in the same process.
Accordingly, in the conventional structure, there has been no method for manufacturing a liquid ejection head capable of reducing the manufacturing processes while maintaining the uniformity of sacrificial layers in the respective substrates taken from the same wafer.